1. Technical Field
This invention relates to the ring-opening metathesis polymerization of norbornene-functional monomers. In particular, this invention relates to a metathesis catalyst system comprising a catalyst and a cocatalyst component. More particularly, this invention relates to novel halogenated organoaluminum cocatalysts that are insensitive to moisture and possess high polymerization activity with long pot life.
2. State of the Art
Methods of polymerizing norbornene-functional monomers such as norbornene, dicyclopentadiene and tetracyclododecene by ring-opening polymerization are well known. Such polymerizations have been carried out in the presence of a metathesis catalyst system comprising a catalyst and cocatalyst component. Suitable catalysts have been selected from molybdenum, tungsten, and tantalum compounds. The cocatalyst includes an organometal compound such as an alkylaluminum, alkylaluminum halide, or alkyltin. Typically, these polymerization reactions are conducted in solution yielding thermoplastic resins, or in in-mold bulk operations yielding tough thermoset products.
In the in-mold bulk polymerization of norbornene functional monomers, the catalyst and cocatalyst components are dissolved in separate aliquots of monomer to form reactant solutions. Reactant streams from each of the catalyst and cocatalyst reactant solutions are mixed to form a monomeric reactive solution which is then conveyed into a closed mold. A chemical reaction occurs in the mold to transform the monomer into the polymeric state. Reaction injection molding (RIM) is a form of in-mold bulk polymerization. Typical RIM molded products include automobile parts such as bumpers, fenders, glove boxes, and the like; pipe couplers; and building panels used in the construction trade.
Recently, the RIM process has been gaining attention for use in the manufacture of large molded parts. U.S. Pat. No. 5,087,343 discloses a RIM process for molding cell heads for electrolytic chlor-alkali cells. While most RIM processes have resulted in good molding with norbornene functional monomers, difficulties have been experienced in molding large parts. A rapid reaction takes place upon mixing of the two reactant streams whereby a polymer barrier forms between the two reactant solutions. Some of the monomer from each reactant stream becomes encapsulated preventing adequate mixing. When molding large parts, extended pot life of the reactive monomer solution is desired. Pot life is defined as the time interval between mixing the reactant streams to form the reactive solution and the point where the solution becomes too viscous (i.e., gels) to adequately fill a mold. After this point the polymerization reaction progresses rapidly and the gel converts to a solid. The premature increase in viscosity of the reaction solution makes it difficult to uniformly convey the reaction solution throughout the mold. This results in molded products with flow marks or weld lines, leading to inferior physical properties.
Early attempts at in-mold bulk polymerization produced reactions that were too rapid and, therefore, uncontrollable. For this reason, methods were proposed to prolong the pot life of in-mold bulk polymerization reactive monomer formulations to prevent premature polymerization. Approaches to improve metathesis catalyst systems by utilizing an ether, ester, ketone, or nitrile in combination with the alkylaluminum cocatalyst have been proposed as disclosed in Japanese Kokai No. 58-129013.
In a further development it has been proposed to alkoxylate or phenoxylate the alkylaluminum cocatalyst in order to reduce the reducing power of the alkylaluminum cocatalyst therefore, extending the pot life of the reactive formulation. Such cocatalysts are disclosed in U.S. Pat. No. 4,426,502.
In in-mold bulk polymerization processes, it also is highly desirable to attain high monomer to polymer conversion. The slightest remnants of unconverted monomer that becomes entrained in the polymer adversely affects the heat resistance of the molded product. Moreover, the entrained monomer continuously volatilizes from the polymer giving off an offensive odor. Unconverted monomer also adversely affects the adhesion of paints and coatings to the surface of the molded product.
For reducing the residual unreacted monomer, the addition of various additives to the reactive formulation have been suggested. Metal and silicon halide additives have been disclosed in Japanese Kokai Nos. 63-186730, 1-301710, 1-126324, and 2-129221. Halohydrocarbon additives have been disclosed in Japanese Kokai Nos. 60-79035 and 1-221416. Halocarboxylic acids have been disclosed in Japanese Kokai No. 63-210122. Carboxylic acid anhydrides have been disclosed in Japanese Kokai No. 63-234021. Phosphorous chlorides have been disclosed in Japanese Kokai No. 1-81818. Sulphur halides have been disclosed in Japanese Kokai No. 1-135829. Among these, most of the metal and silicon halides and the halocarboxylic acids decompose in the presence of moisture, generating hydrochloric acid which corrodes the surface of metal molds. On the other hand, the halohydrocarbons do not present a corrosion problem, however, they are not as efficacious.
Moisture also has been found to adversely affect the activity of the organometallic cocatalyst. This is especially true when employing organoaluminum compounds. Small amounts of moisture contained in the monomer, atmosphere, mold cavity, additives, and the like reacts with the cocatalyst. Consequently, the activity of the cocatalyst diminishes. Moreover, depending on the moisture content of the polymerization system, the activity of the catalyst system will can vary from operation to operation.
Therefore, there is a need for a corrosion inhibiting cocatalyst that imparts a long pot life, provides high monomer conversions, and is moisture insensitive.